Automatic overheat protection for refrigeration system

ABSTRACT

A schematic of an engine driven truck refrigeration system with control circuits is shown. The circuitry provides for automatic shutdown of the refrigeration system should the temperature of the conditioned space exceed a predetermined maximum overheat temperature to thereby prevent a malfunctioning refrigeration system from &#39;&#39;&#39;&#39;cooking&#39;&#39;&#39;&#39; the contents of the conditioned space. A lockout circuit prevents the shutdown circuit from functioning until the control point temperature has been reached or until a defrost mode is initiated so as to permit temperature pull down of the contents of the conditioned space from a temperature exceeding the predetermined maximum overheat temperature.

United States Patent 1151 3,653,223 Jones et al. [45] Apr. 4, 1972 s41 AUTOMATIC OVERHEAT 2,771,748 ll/l956 Prosek ..62/160 PROTECTION FOR REFRIGERATION 2,887,853 /1959 Talmey.. ...62/323 SYSTEM 3,004,399 /1961 Keller ...62/ 160 3,063,251 11/1962 Boehmer ..62/160 [72] Inventors: Daniel F. Jones; David J. Petranek; Harlan 3,1 15,018 12/1963 Inobarry 62/ 1 J. Rosin, all of La Crosse, Wis. P Ex will J w rzma ammer- 1am e [73] Assignee: The Trane Company, La Crosse, Wis. Anomgy Anhur 0 Andersen t Carl M. Lewis [22] Filed: Aug. 31, 1970 [57] ABSTRACT [211 App. No" 68,256 A schematic of an engine driven truck refrigeration system with control circuits is shown. The circuitry provides for auto- [52] U.S.Cl ..62/l60, 62/ 162, 62/229, matic shutdown of the refrigeration system should the tem- 62/230, 62/323, 62/208, 62/151 perature of the conditioned space exceed a predetermined [51] Int. Cl ..F25b 13/00 m xim m overheat temperature to thereby prevent a malss 1 Field of Search ..62/162, 160, 323, 229, 230, functioning refrigeration system from cooking" the contents 2 151 203 of the conditioned space. A lockout circuit prevents the shutdown circuit from functioning until the control point tempera- 56] Referenm m ture has been reached or until a defrost mode is initiated so as to permit temperature pull down of the contents of the condi- UNITED STATES PATENTS tioned space from a temperature exceeding the predetermined maximum overheat temperature. 2,182,691 12/1939 Crago... ..62/ 2,713,247 7/1955 Terry ..62/160 7 Claims, 2 Drawing Figures PATENTEBAFR 4 I972 653 .223

FIG. I

FIG. 2

[NV/:W/ UR. DANIEL F. JONES By DAVID J. PETRANEK HARLAN J. ROSIN ATTORNEY BACKGROUND OF THE INVENTION This invention relates to transportation refrigeration systems and more particularly to those systems used to cool perishable commodities within truck trailers, rail refrigeration cars, and containers.

Commodity transportation refrigeration systems are often provided with means for supplying heat such as to defrost the cooling heat exchanger or to warm the commodity during periods of relatively cool weather. The heat may be supplied by a reverse cycle compression type refrigeration system or simply through the use of hot gas from the refrigeration system compressor or via electric heaters.

Should a failure occur in the refrigeration system which causes the system to remain in the heating or defrosting mode for an extended period, substantial damage may occur to the perishable commodity do to overheating.

SUMMARY OF THE INVENTION The instant invention solves the aforementioned problem by providing a control circuit means which shuts down the system when a predetermined overheat temperature occurs. The overheat temperature is a temperature substantially above the control point temperature at which it is intended that the commodity remain. In most instances shutdown of the system results in less damage to perishable commodities than results from a malfunctioning system which is allowed to remain in the heating or defrost mode. The system thus far described would prevent the temperature pull down of a commodity at a temperature above the predetermined overheat temperature. The instant invention provides circuit means to render the shutdown system ineffective until the control point temperature has been reached or defrost has been initiated.

It is thus an object of the instant invention to provide a means for shutting down a commodity transportation refrigeration system in response to a condition of overheat which may severely damage the commodity.

It is a further object of this invention to provide means for rendering the overheat shutdown system ineffective for a period after the commodity is loaded in the conditioned space.

It is still a further object of this invention to provide means for overriding the overheat shutdown system for a period after the commodity is loaded in the conditioned space until the control point temperature has been reached or until a defrost mode is initiated.

Specifically this invention involves a vehicular refrigeration apparatus comprising: a prime mover; cooling means adapted to be energized by said prime mover for cooling a space within a vehicle; heating means adapted to be energized by said prime mover capable of heating said space; automatic control means for controlling operation of said cooling means, heating means and prime mover means for means for automatically operating said prime mover, cooling actuator means for energizing said cooling means by said prime mover in response to a temperature of said space above a first predetermined temperature, heating actuator means for energizing said heating means by said prime mover in response to a demand for heating, and overheat protector means for discontinuing automatic operation of said prime mover in response to a temperature of said space above a second predetermined temperature higher than said first predetermined temperature; and manual actuator means for rendering said automatic control means operative; said automatic control means further including for temporarily rendering said overheat protector means inoperative following actuation of said manual actuator means thereby permitting said cooling means to initially pull down the temperature of said space from a temperature exceeding said second predetermined temperature.

Other objects and advantages will become more apparent as this specification proceeds to describe the invention with reference to the drawings in which:

FIG. 1 is a schematic of a commodity transportation refrigeration system; and

FIG. 2 is a schematic of a control system for the refrigeration system of FIG. 1.

DETAILED DESCRIPTION Referring now to FIG. 1 of the drawing, the refrigeration system 10 includes a refrigerant compressor 12, a first heat exchanger 13 for exchanging heat between refrigerant and the ambient air, a refrigerant throttling means such as expansion valve 16, and a second heat exchanger for exchanging heat between the refrigerant and the air within the conditioned space 20. The refrigerant compressor 12, first heat exchanger 13, throttling means 16, and second heat exchanger 18, are serially connected in a closed refrigerant circuit 22. Circuit 22 includes an electrically operated reversing valve 24 for reversing the refrigerant flow in circuit 22 exclusive of compressor 12. When the coil 24a is de-energized and compressor 12 is operating, refrigerant is discharged from compressor 12 conducted respectively through reversing valve 24, heat exchanger 14, throttling means 16, heat exchanger 18, reversing valve 24, back to the suction side of compressor 12 whereby heat is removed by heat exchanger 18 from the conditioned space 20 and transferred to the ambient via heat exchanger 13 in a cooling mode. When the coil 24a of reversing valve 24 is energized, refrigerant is discharged from compressor 12 and respectively passes serially through reversing valve 24, heat exchanger 18, throttling means 16, heat exchanger 13, reversing valve 24, back to the suction side of the compressor 12 whereby heat from the ambient is absorbed at heat exchanger 13 and transferred to the air within the conditioned space 20 via heat exchanger 18 in a heating mode.

Fans 26 and 28 are positioned respectively to pass air from the ambient and conditioned space in heat exchange relationship with heat exchangers 13 and 18. A diesel engine 30 is appropriately drivingly connected to compressor 12 via shaft 32. Fans 26 and 28 are drivingly connected to shaft 32 via sheaves 34 and belt 36. The drive shaft of fan 28 is provided with an electromagnetic clutch 38 which is engaged when coil 38a thereof is energized. Engine 30 has a fuel supply valve 40 which is opened by energization of fuel supply valve coil 40a. Engine 30 also includes a starter motor 42 drivingly connected to shaft 32. FIG. 1 also discloses elements of the control system including temperature controller thermostat 14, overheat sensing thermostat 46, differential pressure switch 48 for initiating the frost on heat exchanger 18, and defrost termination switch 50 responsive to temperature of heat exchanger 18. Thermostat 14 preferably has an adjustable control point between the temperatures of l0 F. and F. Overheat thermostat 46 may be set to open at temperatures in excess of F. Pressure differential switch 48 is arranged to close when the pressure differential across heat exchanger 18 indicates a need for defrost. Defrost termination switch 50 is set to open in response to a heat exchanger temperature indicative of completed defrost.

The operation of the refrigeration system shown in FIG. I may be best understood by reference to the electrical circuit shown in FIG. 2. In addition to the elements shown in FIG. 1 the circuit of FIG. 2 includes a battery power source 52, a system manual on-off switch 54, a manually operated normally open starter switch 56, starter solenoid 58 controlling normally open switch 58a, temperature control relay 60 controlling normally open switch 60a, defrost relay 62 controlling normally open switch 62a, normally closed switch 62b and normally open switch 62c, overheat protector relay 64 for controlling normally closed switches 64a and 64b and normally open switch 640, manually operated defrost initiating switch 66, and manually operated overheat protector disabling switch 68.

Now let it be assumed that manually operated switch 66 is open and that manually operated switch 68 is closed. Let it further be assumed that the temperature within the conditioned space 20 is above 75 F. whereby the overheat thermostat 46 is open. Upon closing switch 54 a first circuit is established including switch 54, switch 640, and coil 40a of fuel supply valve 40 thereby opening fuel supply valve 40. Also a second circuit is established including switch 54, switch 621), and coil 38a thereby engaging clutch 38. Momentary closure of starter switch 56 momentarily establishes a circuit including switch 54, switch 64a, and switch 56, and starter solenoid 58 which in turn momentarily closes normally open starter solenoid switch 58a to momentarily energize starter 42 thereby starting engine 30 which drives compressor 12 and fans 26 and 28.

Should the temperature within the conditioned space 20 be above the control point of thermostat 14, thermostat 14 remains open and the temperature control relay 60 de-energized whereby the system is operated in the cooling mode to cool conditioned space 20.

When the conditioned space 20 has been cooled to the set point of thermostat 14, thermostat 14 is closed establishing a circuit including thermostat 14 and temperature control relay 60 thereby closing normally open switch 60a to energize a circuit including switch 62b, 60a, and coil 24a of reversing valve 24 to change the system from a cooling mode to a heating mode. The closure of switch 60a when the set point temperature of thermostat 14 has been reached, also establishes a circuit including switch 6217, switch 60a, switch 64b, overheat protector relay 64 and switch 68 whereby overheat protector relay 64 is energized to close switch 64c and open switches 64a and 64b. The closure of switch 64c establishes an overheat protector relay holding circuit including switch 640, relay 64, and switch 68 to hold overheat protection relay 64 in the energized position until either of switches 54 or 68 are manually opened. The opening of normally closed switch 64a requires coil 40a of fuel supply valve 40 to be.energized solely through a circuit including thermostat 46 which shunts now open switch 64c. Should the temperature of the conditioned space exceed the set point of overheat thermostat 46 (75 F), such as by a malfunction causing continuous operation in the heating mode, thermostat 46 will open thereby de-energizing coil 40a of fuel valve 40 to thereby shut down the refrigeration system. In other words, any failure of the system to maintain the temperature of the conditioned space below the set point of overheat thermostat 46 (75 F) after the initial pull down period will cause the system to shut down due to overtemperature. However, means namely 64a is provided for overriding the overtemperature shutdown system for a period from starting of the system until the control point temperature of thermostat 14 has been reached.

Now let it be assumed that the thermostat 14 is open, temperature control relay 60 de-energized, switch 600 open, overheat protection relay 64 energized, switches 64a and 64b open, and switch 640 closed. No circuit is established through coil 24a of reversing valve 24 whereby the system remains in the cooling mode. Should sufficient frost accumulate on the heat exchanger 18 to establish a predetermined pressure differential between the upstream and downstream sides thereof, differential pressure switch 48 for initiating the defrost of heat exchanger 18 will be closed thereby establishing a circuit including switch 48, defrost relay 62 and defrost termination switch 50. Energization of defrost relay 62 closes normally open switch 620, opens normally closed switch 62b, and closes normally open switch 620. The closure of switch 62a establishes a defrost relay holding circuit including switch 62a, defrost relay 62 and defrost termination switch 50* whereby defrost relay 62 remains energized until the opening of switch 50. The opening of switch 62b de-energizes the circuit including switch 62b and coil 38a of clutch 38 thereby disengaging clutch 38 and disengaging fan 28 during the defrost mode. Closure of switch 62: energizes a circuit including switch 62c and the coil 24a of reversing valve 24 thereby reversing the refrigerant circuit 22 to supply hot compressed refrigerant gas to heat exchanger 18 whereby the frost accumulated thereon is melted. This defrost mode may be initiated manually if desired by momentarily closing switch 66. The defrost mode is terminated when the temperature of heat exchanger 18 rises to a predetermined level indicative of complete frost removal therefrom as sensed by defrost termination switch 50. Upon the opening of switch 50 defrost relay 62 is de-energized thereby closing switches 62a and 62c and opening switch 62b thus energizing coil 38a of clutch 38 and de-energizing coil 24a of reversing valve 24 to resume the cooling mode. It should be observed that closure of switch 62c when the defrost mode is initiated also establishes a circuit including switch 62c, switch 64b, overheat protector relay 64 and switch 68 whereby overheat protector relay 64 is energized to close switch 64c and open switches 64a and 64b. The closure of switch 641 establishes an overheat protector relay holding circuit including switch 640, relay 64, and switch 68 to hold overheat protector relay 64in the energized position until either of switches 54 or 68 are manually opened. The opening of normally closed switch 64a requires coil 40a of fuel supply valve 40 to be energized solely through a circuit including overheat thermostat 46 which shunts now open switch 640. Should the temperature of the conditioned space exceed the set point of overheat thermostat 46 (75 P), such as by a malfunction causing continuous operation of the defrost mode, thermostat 46 will open thereby de-energizing coil 40a of fuel valve 40 to thereby shut down the refrigeration system.

Furthermore, should the temperature of the conditioned space rise above the set point of overheat thermostat switch 46 (75 F) during the cooling mode of operation after the temperature of the conditioned space 20 has once reached the set point of thermostat 14, the opening of switch 46 will also cause de-energization of coil 40a of fuel supply valve 40 thereby shutting the system down.

Thus it will be seen that at any time after the temperature within the conditioned space 20 has once reached the set point of thermostat 14 or after defrost is first initiated, whether the system be operating in the defrost, cooling, or heating modes, the system will be shut down in response to dangerously high overtemperatures within the conditioned space. On the other hand, means is provided for overriding the shutdown system until the temperature within the conditioned space 20 has first reached the set point or is first defrosted thereby enabling the temperature of an exceedingly warm load to be pulled down to the set point.

Having now described the preferred embodiment of our invention, we contemplate that many changes may be made without departing from the scope or spirit of our invention, and we accordingly desire to be limited only by the claims.

We claim:

1. A vehicular refrigeration apparatus comprising: a prime mover; cooling means adapted to be energized by said prime mover for cooling a space within a vehicle; heating means adapted to be energized by said prime mover capable of heating said space; automatic control means for controlling operation of said cooling means, heating means and prime mover including means for automatically operating said prime mover, cooling actuator means for energizing said cooling means by said prime mover in response to a temperature of said space above a first predetermined temperature, heating actuator means for energizing said heating means by said prime mover in response to a demand for heating, and overheat protector means for discontinuing automatic operation of said prime mover in response to a temperature of said space above a second predetermined temperature higher than said first predetennined temperature; and manual actuator means for rendering said automatic control means operative; said automatic control means further including means for temporarily rendering said overheat protector means inoperative following actuation of said manual actuator means thereby permitting said cooling means to initially pull down the temperature of said space from a temperature exceeding said second predetermined temperature.

2. The apparatus as defined by claim 1 wherein said overheat protector means is rendered inoperative until operation of said heat actuator means.

3. The apparatus as defined by claim 1 wherein said overheat protector means is rendered inoperative until said cooling means is actuated to a noncooling cycle.

4. A refrigeration apparatus for cooling a conditioned space comprising: a refrigerant circuit including; a refrigerant compressor, a first heat exchanger disposed in heat exchange relationship with outdoor ambient air, a refrigerant throttling means, and a second heat exchanger disposed in heat exchange relationship with said conditioned space; means for directing refrigerant respectively through said compressor, said first heat exchanger, said throttling means, and said second heat exchanger back to said compressor whereby said refrigeration apparatus is operated in a cooling mode to cool said conditioned space; control means responsive to the temperature of said conditioned space for cycling said refrigeration apparatus to and from said cooling mode for maintaining the temperature in said conditioned space substantially at a predetermined first temperature; said refrigerant circuit including means for supplying hot refrigerant from said compressor to said second heat exchanger for warming said second heat exchanger; and means de-energizing said compressor in response to a second predetermined temperature of said conditioned space higher than said first predetermined temperature.

5. Refrigeration apparatus comprising means for controlling the temperature of a space; disrupting means responsive to the temperature of said space for disrupting operation of said temperature controlling means in response to a predetermined abnormally high temperature indicative of a failure of said temperature controlling means and; means for automatically overriding said disrupting means whereby said temperature controlling means may be operated to pull down the temperature of said space from a temperature in excess of said predetermined abnormally high temperature.

6. In a prime mover powered compression cycle refrigeration system having both heating and cooling cycles for conditioning a space, the improvement comprising: a first circuit including a temperature responsive overheat switch responsive to the temperature of said conditioned space for energizing said prime mover; a second circuit including a cycle selector means and a thermostat responsive to the temperature of said conditioned space; and a third circuit responsive to the operating condition of said second circuit including a relay having a first switch shunting said overheat switch and a second switch for holding said relay energized after interruption of said third circuit.

7. The apparatus as defined by claim 4 including means for automatically overriding said means for de-energizing said compressor whereby said refrigeration apparatus may be operated to pull down the temperature of said conditioned space from a temperature in excess of said predetermined temperature. 

1. A vehicular refrigeration apparatus comprising: a prime mover; cooling means adapted to be energized by said prime mover for cooling a space within a vehicle; heating means adapted to be energized by said prime mover capable of heating said space; automatic control means for controlling operation of said cooling means, heating means and prime mover including means for automatically operating said prime mover, cooling actuator means for energizing said cooling means by said prime mover in response to a temperature of said space above a first predetermined temperature, heating actuator means for energizing said heating means by said prime mover in response to a demand for heating, and overheat protector means for discontinuing automatic operation of said prime mover in response to a temperature of said space above a second predetermined temperature higher than said first predetermined temperature; and manual actuator means for rendering said automatic control means operative; said automatic control means further including means for temporarily rendering said overheat protector means inoperative following actuation of said manual actuator means thereby permitting said cooling means to initially pull down the temperature of said space from a temperature exceeding said second predetermined temperature.
 2. The apparatus as defined by claim 1 wherein said overheat protector means is rendered inoperative until operation of said heat actuator means.
 3. The apparatus as defined by claim 1 wherein said overheat protector means is rendered inoperative until said cooling means is actuated to a noncooling cycle.
 4. A refrigeration apparatus for cooling a conditioned space comprising: a refrigerant circuit including; a refrigerant compressor, a first heat exchanger disposed in heat exchange relationship with outdoor ambient air, a refrigerant throttling means, and a second heat exchanger disposed in heat exchange relationship with said conditioned space; means for directing refrigerant respectively through said compressor, said first heat exchanger, said throttling means, and said second heat exchanger back to said compressor whereby said refrigeration apparatus is operated in a cooling mode to cool said conditioned space; control means responsive to the temperature of said conditioned space for cycling said refrigeration apparatus to and from said cooling mode for maintaining the temperature in said conditioned space substantially at a predetermined first temperature; said refrigerant circuit including means for supplying hot refrigerant from said compressor to said second heat exchanger for warming said second heat exchanger; and means de-energizing said compressor in response to a second predetermined temperature of said conditioned space higher than said first predetermined temperature.
 5. Refrigeration apparatus comprising means for controlling the temperature of a space; disrupting means responsive to the temperature of said space for disrupting operation of said temperatUre controlling means in response to a predetermined abnormally high temperature indicative of a failure of said temperature controlling means and; means for automatically overriding said disrupting means whereby said temperature controlling means may be operated to pull down the temperature of said space from a temperature in excess of said predetermined abnormally high temperature.
 6. In a prime mover powered compression cycle refrigeration system having both heating and cooling cycles for conditioning a space, the improvement comprising: a first circuit including a temperature responsive overheat switch responsive to the temperature of said conditioned space for energizing said prime mover; a second circuit including a cycle selector means and a thermostat responsive to the temperature of said conditioned space; and a third circuit responsive to the operating condition of said second circuit including a relay having a first switch shunting said overheat switch and a second switch for holding said relay energized after interruption of said third circuit.
 7. The apparatus as defined by claim 4 including means for automatically overriding said means for de-energizing said compressor whereby said refrigeration apparatus may be operated to pull down the temperature of said conditioned space from a temperature in excess of said predetermined temperature. 